1. Field of the Invention
This invention is concerned with improving the operation of cyclone separators used to separate finely divided fluidizable catalyst particles from gasiform reaction products. More particularly, the invention is concerned with the method and means for improving the operability and dependability of cyclonic separation equipment commonly used in chemical operations, e.g., in fluid catalytic cracking (FCC) processes.
2. Description of the Prior Art
In the cyclone type of separator, a suspension comprising a gasiform material with entrained finely divided solid material is introduced into the separator in a tangential manner that imparts a spiral or centrifugal swirling motion or action to the suspension. The centrifugal action causes the solids to be thrown to the outer wall of the cyclone separator, and they then slide down the cyclone wall into a solids dust hopper therebelow for withdrawal therefrom, e.g., by a standpipe or dipleg means. The gasiform material thus separated from the solids is removed by a central open passageway extending from a plane beneath the suspension tangential inlet upwardly through the top of the cyclone separator.
The cyclones are particularly useful in connection with organic reactions employing fluidizable catalyst particles, such as in the catalytic treatment of petroleum fractions by cracking, the synthesis of hydrocarbons from carbon monoxide and hydrogen, the conversion of methanol to liquid hydrocarbons or other fluid catalyst operations known in the art.
In modern operations, such as riser catalytic cracking operations, enormous amounts of solid catalyst particles suspended in gasiform materials are handled in riser catalytic cracking units and it is necessary to rapidly separate the suspensions into a catalyst phase and a gasiform phase after the suspension from the conversion operation has traversed the riser unit or conversion zone.
The dipleg or standpipe means of the cyclone is usually equipped with a valve means which allows the accumulated solid catalyst particles to be discharged into the space below the dipleg into the containing vessel once the weight of the accumulated particles in the dipleg reaches a predetermined limit. The valve means may sometimes be equipped with a counterweight to regulate the weight of the solid particles necessary to open the valve means. The most common types of valves used for that purpose are trickle valves, flapper valves and flapper valves with a counterweight, the weight of which may be adjusted for a particular application. A typical flapper valve equipped with a counterweight is illustrated in FIG. 1. Other trickle and flapper valves, with and without counterweights, are shown and discussed in Zenz and Othmer, "Fluidization and Fluid Particles Systems", Rheinhold Publishing Corporation, 1960, pages 410-415, and in the article by F. A. Zenz, "Cyclone Collectors," a Particulate Solids Research, Inc. publication, State of the Art-24, July 1, 1981, pages 2-82 through 2-94, the entire contents of both being incorporated herein by reference.
The flapper valve positioned perpendicularly to the standpipe (shown in FIG. 1) is a commonly used valve in FCC installations, both in the reactor vessels and in the regenerator vessels. The flapper valve is usually equipped with a counterweight, as discussed above.
Modern designs for reactor and regenerator vessels of the FCC installations incorporate a dense and dilute fluidized phases. For example, in the regenerator vessel of the fast fluidized bed regenerator (described, e.g., by Gross et al. in U.S. Pat. No. 4,118,338, the entire contents of which are incorporated herein by reference) the inner bed of spent catalyst comprises a primarily dilute fast fluidized phase in the lower regenerator vessel, while the outer bed of regenerated catalyst is a dense fluidized phase. Final separation of the flue gas from catalyst takes place in cyclones usually arranged in several sets of two in series, located in a second dilute phase in the upper regenerator, and above the dense bed. The two cyclone stages in series are usually referred to as primary and secondary cyclones. Both sets of cyclones have diplegs which usually terminate in the second dilute phase, returning catalyst particles therefrom by free-fall to the dense bed below. The flapper valves placed perpendicular against the bottoms of the diplegs and equipped with the counterweights properly serve their function in the second dilute phase. A substantial volume of catalyst is usually conducted through the diplegs from the primary cyclones. The relatively large flow rate of the catalyst prevents any solid particles (e.g., coke or a piece of refactory) from being wedged between the valve plate and the end of the dipleg.
However, in the diplegs of the secondary cyclones, where the flow rate of the catalyst is substantially lower than in the primary cyclone diplegs, solid particles are often lodged between the horizontal plate of the valve and the bottom of the dipleg, thereby jamming the valve in the opened position, as illustrated in FIG. 1A. The jammed valve allows process gases to travel up through the dipleg and out of the cyclone, carrying with them small fine particles of catalyst. In the regenerator vessel, the catalyst-containing gas carries the solid catalyst particles out through the stack and into the atmosphere. The increased particulate content of the stack gas may violate environmental regulations. In the reactor vessel, the catalyst-containing gas may carry the solid catalyst particles into the main fractionation column, thereby fouling it and disrupting the operation of the column and of other downstream equipment.
Accordingly, it is a primary object of the present invention to provide an improved flapper valve means for cyclone diplegs.
It is an additional object of the present invention to provide a flapper valve for cyclone diplegs which prevents or substantially eliminates the risk of solid particles lodging in-between the plate of the valve and the outlet of the dipleg.
Additional objects of the invention will become apparent to those skilled in the art from the specification and the appended claims.